This study evaluates the impact of autologous 'leucocyte and platelet rich fibrin' (L-PRF) on the periapical bone healing and further root development of infected immature permanent teeth. In the test group regenerative endodontic procedure (REP) is performed with L-PRF as scaffold, in the control group REP without L-PRF is performed .

Regenerative endodontic procedures are biologically based procedures designed to restore function of a damaged and nonfunctioning pulp by stimulation of existing stem and progenitor cells present in the root canal and/or the introduction and stimulation of new stem and dental pulp progenitor cells into the root canal under conditions that are favorable to their differentiation and reestablishment of function. L-PRF has the potential advantage of creating a bioactive construct that stimulates the local environment for differentiation and proliferation of these stem and progenitor cells. We have designed this confirmatory study to test the hypothesis that the use of L-PRF in REP of infected permanent immature teeth will accelerate periapical bone healing and stimulate the root maturation.

Inclusion Criteria:

• Provision of Informed Consent
• Permanent immature teeth with weak root canal walls (hopeless prognosis)
• Patients younger than 25 years

Exclusion Criteria:

• - Unlikely to be able to comply with the study procedures, as judged by the investigator.
• Patients older than 25 years
• Deciduous teeth
• Permanent (immature) teeth that can be treated by a "regular" root canal treatment/ apexification
• Known or suspected current malignancy
• History of chemotherapy within 5 years prior to study
• History of radiation in the head and neck region
• History of other metabolic bone diseases
• A medical history that makes REP unfavorable
• Involvement in the planning and conduct of the study
• Previous enrolment in the present study